This paper is a summary of a four-volume report entitled Analysis
of Dualmode Systems in an Urban Area (DOT-TSC-OST-73-16A-1), published in 1973.
All of the documents are available from the National Technical Information Service, Springfield, VA, 22151. This paper was originally published in the Proceedings from a
conference entitled Personal Rapid Transit II: Progress, Problems, Potential,
University of Minnesota, December, 1973, pp 95-106.
[Updates shown in red text]

The automobile provides convenient, flexible, relatively low-cost transportation, and
is thus the overwhelming choice of urban travelers. Currently, increasing concern is being
voiced over relatively uncontrolled growth of automobile travel. Noise and air pollution,
the divisive effect of ribbons of concrete cutting through neighborhoods and the plight of
minority groups and the poor traditionally displaced by new urban freeways are being
recognized. Consequently, public pressure has developed in opposition to new highway
construction. In fact, in a number of urban areas, new roadway construction has come to a
virtual standstill.

While demand for transportation continues to grow, conventional transit systems have
been unable to attract significant ridership or provide the service desired by travelers.
What is needed is a transportation system with the apparent advantages of the automobile
but without the associated congestion, pollution or large right-of-way requirements.

Dualmode transportation systems have been suggested as alternative transportation forms
with the potential to meet this need. A dualmode vehicle is one which travels under manual
control on the street network for some portion of its trip, and operates under automatic
control on an exclusive guideway for some other portion. Thus low density
collection/distribution functions could be accommodated at low capital cost using existing
street facilities, while high-density routes with common origins and destinations for many
travelers could be automated.

Automation provides the potential for: 1) achieving increased guideway capacity through
close-headway operation, 2) allowing safe high-speed travel without congestion, and 3)
providing increased free or productive time to drivers by relieving them of their duties.
Electrically powered dualmode vehicles may help to reduce air pollution, and guideway
design may permit minimization of noise transmission to adjoining areas. Dualmode
transportation systems have the potential to provide door-to-door transportation
equivalent to the automobile in convenience, and thereby may attract ridership from
highways and reduce the problems of congestion.

The U.S. Department of Transportation, through the Systems Analysis Division of the
Transportation Systems Center has conducted an economic feasibility analysis of dualmode
transportation systems in order to provide information upon which to base research and
development priority decisions.

The analysis was conducted in a 1990 Boston scenario, in which an extensive dualmode
system was presumed to exist. The scenario was chosen only to provide meaningful base
data. The study was not a proposal for a dualmode system in Boston or a transportation
plan for that area. As a basis for comparison a 1990 transportation plan for Boston
projected by the Eastern Massachusetts Regional Planning Project was also analyzed. The
analysis was oriented toward examining urban-wide applications of the dualmode concept, as
opposed to limited-service systems for specific purposes.

For the purposes of the analysis, performance levels were specified with the assumption
that the appropriate technologies (such as command and control) would be developed
sufficiently to permit their attainment. Continued technological development is required
to achieve these capabilities.

BASELINE DESCRIPTIONS

The proposals for dualmode systems that have been made by various institutions,
companies, and developers were examined for their basic technological and application
elements. These basic elements were categorized and grouped according to common
characteristics, from which evolved generic baselines which represent classes of
proposals. Each of the baselines discussed herein consists of a combination of personal
vehicles and buses, thereby providing the user with alternative choices in using the
system.

The three baselines examined in this report in detail are described in Figure 1. The pallet
system consists of conventional private automobiles which are driven onto pallets
that operate on the guideway, and 20-passenger buses which do not use pallets but
interface directly with the guideway. [For
a current example of a pallet (or car ferry) system, being developed, see the
MegaRail website]

A typical trip on the system is depicted in Figure 2
[updated with RUF vehicles by Palle Jensen]. A standard
automobile is driven manually on the street network to the guideway entrance. The car is
then driven onto the pallet which operates automatic control on the guideway. If the
destination is outside of the urban core, the car is driven off the pallet at the
appropriate exit and then manually operated on the streets to the destination. The already
extremely congested downtown area of Boston does not rationally invite discharging large
numbers of dualmode vehicles onto the streets. Consequently, no exit from the system is
permitted in this area. Upon arriving at an urban-core station, the automobiles are
unloaded from the pallets and are parked in garages, with no street access permitted. The
riders then walk to their destinations or transfer at the garage to the existing local
transit system for downtown collection and distribution.

The buses were assumed to operate on fixed routes and schedules on the streets in the
suburbs. Upon entry to the guideway, the driver leaves the vehicle and it operates
automatically. In the downtown area, transfer to transit it required.

The automated-highway baseline consists of: 1) automobiles in their
automated mode, interfaced directly with guideway, and 2) buses which operate in the same
fashion as the pallet-system buses. 0ff the guideway the autos perform in the conventional
manual mode. [For a current example being developed, see
the 9-minute Qwiklane video]

The new small-vehicle baseline consists of: 1) innovative small
personal vehicles specifically designed for operation, and 2) dualmode 12-passenger
minibuses. In this case a dense guideway network with stations easily accessible by
walking is provided in the central business district, thereby eliminating the downtown
transfer to transit. The small personal vehicle is designed for individual use, but is
owned by and rented from the system. [For current examples
being developed, see the Personal Rapid Transit and
Dualmode overview webpages]

As shown in Figure 2,
[updated with RUF vehicles, by Palle Jensen] for suburban collection the vehicle is driven manually to the closest station, and if the
destination is in the downtown area the user leaves the vehicle upon arrival at the
station closest to the intended destination. For a return trip, a vehicle, but not
necessarily the same one driven in, is provided at whichever downtown station is chosen.
Thus a vehicle is always guaranteed at a downtown station, but no permanent correlation
between particular individuals and vehicles exists. The minibus operates as a dial-a-ride
vehicle in the suburbs. [An excellent current
example is the Danish RUF dualmode system]

NETWORK DESCRIPTION

A single dualmode guideway network was designed for all baselines, with some
adjustments required to meet the peculiarities of specific systems, particularly in the
downtown area. In keeping with the objective of minimizing community disruption, an
attempt was made to use existing rights-of-way whenever possible.

The dualmode guideway network designed for the Boston scenario is depicted in
Figure 3. Most of the
stations, shown as circles, provide for entry to and exit from the system. Stations in and
near the central core are indicated as three different types. The squares are stations
where dualmode users interface directly with existing Boston rapid transit systems. Exit
from and entry to the street network is provided, and parking at the station is encouraged
by reduced parking costs. The stations indicated by the diamonds permit only parking and a
transit interchange, with no street access. To discourage parking in areas of higher land
cost, higher parking rates were established at these stations. The one station shown with
a triangle has no transit interface, but is within walking distance of the main financial
district. The new small-vehicle system substituted a dense network in the downtown area as
shown in Figure 4.

RESULTS

Intuitive analyses of various systems indicated that for urban-wide applications, mixed
vehicle fleets are more attractive than either personal dualmode vehicles or dualmode bus
systems alone. In all cases examined, mixed fleets provided greater ridership and higher
revenues as well as lower cost per passenger trip than single vehicle systems. The bus
systems provide service for the "transportation poor" while the personal
vehicles maximize the diversion of travelers from the highway onto the guideway. The mixed
fleet not only provides a logical implementation sequence, starting with the bus and then
adding the more complex operations of personal vehicles; but also, provides the
flexibility to meet changing patterns of transportation demand.

Service

The service levels achieved by the three dualmode baselines and by the l990 plan are
compared in Figure 5. All of the dualmode systems attained more than a 10% modal
split--more than the transit split in the case. Since less than half of the trips in the
region are of sufficient length or are located so that they are candidate dualmode trips,
the 16% split attained by the new small-vehicle baseline actually represents the
attraction of more than 30% of the potential dualmode users. Dualmode attracts as much as
53% of the peak-hour downtown-bound travelers. Although the transit and dualmode systems
were designed to be complementary, considerable competitive characteristics remained.
Therefore, the dualmode systems might be expected to fare even better in other scenarios
without the large existing investment in transit.

The diversion of riders from the highways onto the dualmode guideway reduced highway
traffic congestion, as evidenced by an increased peak-period surface arterial speed. The
dualmode systems themselves achieved as much as a 57% increase in door-to-door travel
speed compared with a similar trip under the 1990 plan. For a typical dualmode trip the
average user saved in the vicinity of 15 to 20 minutes compared with the trip he would
have taken if the 1990 plan had been adopted. The combination of reduced highway
congestion and generally higher average speed of dualmode travel resulted in the saving of
as much as 36 years of travel time every day.

Costs

The total capital cost of the urban-wide implementation in the Boston scenario of the
various dualmode baselines ranged from 1.6 billion dollars to more than four billion
dollars, as shown in Figure 6. Smaller systems could be constructed at proportionately
lower costs. Just over one billion dollars (in the form of 114 miles (71 km) of highway
and 29 miles (18 km) of rapid transit extension) of proposed construction in the 1990 plan
would not be built if dualmode were installed. This, in effect, represents a capital cost
savings incurred by the adoption of a dualmode system.

The purchase price of 420,000 system-owned small personal vehicles accounts for nearly
half the capital cost of new small-vehicles. In this baseline a significant benefit
accrues to the large number of users who rent a dualmode vehicle and forego the purchase
of a second family car. For the automated highway, the system vehicle capital costs
include only the purchase of buses, since the personal vehicles are privately owned and
operated. Both pallets and buses are included in the vehicle cost for the pallet system.

Capital costs were annualized by applying a 10% interest rate and depreciating each
individual element of each system over its lifetime. Total annual dualmode capital and
operating cost reflects total door-to-door transportation costs to society, including such
items as the operating and depreciation costs of private vehicles during the off-guideway
portions of pallet or automated highway dualmode trips. They range from a low of just over
600 million dollars to almost one billion dollars, with the variation largely representing
differences in service levels and ridership. The annual costs per passenger trip for all
systems were approximately the same.

Figure 7 shows how
the profits and losses of the system operator would change with variations of up to 25%
from the nominal assumed fare levels. Revenues of all systems can equal or exceed
operating costs, but local capital subsidies would be required to meet total system costs.

Impacts

Figure 6 also compares some of the regional impacts of the various dualmode
alternatives and of the 1990 plan. The pollution output associated with the generation of
electrical power for the pallet and new small-vehicle baselines was included in the
figures, which are for all transportation modes in the region. The high power requirements
of the pallet alternative caused by the necessity to move heavy pallets and the vehicles
on them, as well as empty pallets, resulted in the pollution levels of this baseline
exceeding the 1990 plan. Longer trip lengths, high speed operation, and diversion from
transit caused the automated-highway vehicles, powered by internal combustion engines, to
contribute to a greater total pollution level than the l990 plan. The only significant
reductions in pollution levels were achieved by the new small vehicles.

Most of the route miles of the systems analyzed in this scenario were accommodated on
existing rights of way or were tunneled. Dualmode systems, with twice the route mileage of
planned highway and transit additions, displaced only 10% of the number of families which
the 1990 plan of construction would have moved. Although the pallet and automated-highway
vehicle baselines had fewer route miles than the new small-vehicle baseline, the former
required large parking garages for the storage of private vehicles, thereby causing
somewhat greater displacements. Largely because of guideway structure and location
dualmode systems caused only 1% of the noise impacts associated with the 1990 plan. Thus,
at a time when community pressures are making acquisition of new right of way for
transportation systems increasingly difficult, dualmode systems can significantly reduce
neighborhood disruption and division as well as avoid the displacement of minority groups
and low income families--the traditional victims of new transportation system
construction.

Cost and Benefits

The annual costs and benefits of the dualmode alternatives relative to the 1990 plan
are summarized in Figure 8.
Costs and benefits were calculated on a regional basis for all transportation modes. Thus
the costs include dualmode operating costs and annual capital debt service, differential
cost savings due to reduced highway and transit construction and maintenance, and changes
in the costs incurred by individual motorists operating their vehicles. The benefits
costed include travel time savings, relocation savings, accident savings, changes in
pollution costs, and changes in land values and tax revenues. They do not include benefits
from such items as decreased neighborhood intrusion, additional job accessibility, or
regional economic stimulation, which either could not be adequately quantified, or were
considered un-costable. The 1990 plan was used as a base, and all costs incurred beyond
that level and all benefits obtained above that base were included.

Figure 8 shows that
the regional benefits of the mixed-vehicle dualmode systems, for urban-wide applications,
are more than twice the costs. Of the systems analyzed, the new small-vehicle system has
the greatest total benefits, the largest net benefits, and the highest ratio of benefits
to costs. Moreover, this baseline attracts the highest level of ridership, and revenues
exceed the operating costs by the greatest increment. It obtains this, however, at the
highest capital cost of any baseline and thus requires the biggest capital subsidy. These
capital costs, although quite large, are not inconsistent with the costs of any large
urban transportation system, and on a route-mile basis are lower than those of the New
York Second Avenue Subway and the projected unit costs of the Washington, D.C. (METRO),
Baltimore, and Atlanta rapid transit systems.

Because of the generally conservative assumptions used in this analysis, the results
presented tend, except where noted, to project a conservative case for the dualmode
systems. As parametric analyses indicated, more optimistic projections would improve the
general picture, although the relative results (differences between alternatives) would
not be expected to change significantly.

SYSTEM IMPLEMENTATION

Urban-wide applications of dualmode transportation systems were considered in this
analysis. However, such systems will not come into existence instantaneously; rather they
will grow over a period of years. Because the system characteristics will change during
this implementation period, various dualmode alternatives will provide the greatest
effectiveness at each stage.

Initial implementation of dualmode will, in all probability, occur in a high-demand
density corridor. The limited extent of the guideway and restricted number of origins and
destinations would tend to discourage the purchase or rental of personal dualmode
vehicles. Thus, if personal vehicles are to be used in a limited-scale system, the pallet
would appear most appropriate alternative.

A limited corridor with relatively high demand occurring between common origins and
destinations permits the attraction of sufficient ridership and the achievement of high
enough load factors to make bus systems very effective. The low vehicle capital and
operating costs per passenger mile of bus systems with high load factors in such limited
applications provide the opportunity to install a working dualmode system at minimal cost
and still achieve acceptable ridership.

Because dualmode buses can be operated on guideways at relatively large headways
compared to those required to move the same volume of people in personal vehicles, bus
systems would appear ideal for the initial developmental stages of these systems, when
command and control technology is in its early stages of maturity. Of the bus systems
examined, the minibus with dial-a-ride service achieved the greatest ridership, and would
appear to be most suitable for an initial dualmode application. Personal vehicles could be
introduced at a later date to increase utilization of the guideway, with the pallet being
the most attractive candidate so long as a limited diversity of origins and destinations
is available.

This analysis suggests that as the network expands, the new small-vehicle alternative,
in scenarios similar to Boston, provides the greatest benefit/cost ratio. If sufficient
funds are not available for implementation of this alternative, continued expansion of the
pallet or introduction of the personal automated-highway vehicle may be preferred, despite
their slightly lower benefit/cost relationship. Were the new small-vehicle system to be
implemented, however, continued use of pallets or pallet-like vehicles for freight would
be desired to further diversify system usage.

The introduction, at a later stage, of a coordinated off-guideway non-dualmode
dial-a-ride bus feeder and on-guideway personal vehicle (PRT) system has the potential to
further increase ridership while decreasing costs per passenger trip through increased bus
load factors. The evolution of an urban-wide application of dualmode transportation,
therefore, would utilize a number of the concepts examined during its various stages of
growth.

CONCLUSIONS

Although this analysis was conducted in the Boston scenario, these conclusions are
considered to apply to many other large urban areas as well:

dualmode systems appear to be sufficiently attractive to warrant further technological
development.

For urban-wide applications, dualmode systems which include mixtures of buses and
personal vehicles are more effective than either fleet alone

A dualmode transportation system benefits from the use of various dualmode concepts
throughout its development

For the first stage of implementation of a dualmode network, the dualmode minibus seems
most effective. Capability should be provided for subsequent expansion to the use of
personal vehicles and buses

The results presented here are for only one scenario and for urban-wide implementation
of the concept. It is expected that different demand patterns, population densities, and
urban forms would lead to some differences from the results obtained in this analysis. The
rather extensive rail rapid transit system in existence in Boston, together with the
extremely dense central business district having poor surface arterial circulation, forced
the network design and operating policies for the alternatives examined to be considerably
different from those which would be expected in other scenarios. The prohibition or
dualmode vehicles from the downtown streets would probably not be necessary in cities with
a lower population density and better central business district arterial circulation. The
differentially priced downtown and peripheral parking with transfer to transit might not
be as desirable elsewhere, nor would the extensive tunneling for the downtown network
necessarily be required. In Boston the analysis examined dual mode and transit as
complementary, but also competing modes. This would not be the case in cities which do not
have an existing investment in rapid transit.

An overview of current dualmode development projects
and issues is provided by a Dualmode overview
webpage and a Dualmode Debate webpage. A major
Dualmode Study performed at the Texas A&M University by the Center for
Environment, Energy and Innovative
Transportation (CEETI) is also available on-line. A link to it is provided at
the Dualmode overview webpage.